It is known to extract bromine from seawater or aqueous solutions containing bromide ions, by oxidizing the bromide ions. The preferred oxidizing agent is generally chlorine. Thus British Pat. No. 523,607 describes a procedure having the following steps:
(A) Oxidation by chlorine of sodium bromide from seawater previously brought to a pH equal to 3.5.
(B) Degassing of bromine from this solution by air.
(C) Fixation of the bromine vapors by sulfur dioxide to form a so-called "bromosulfuric" solution containing 120-150 grams/liter of hydrobromic acid.
(D) Extraction of bromine from this solution by the action of a new quantity of chlorine and sweeping out the vapor.
The use of chlorine, particularly for the last of these steps, presents several disadvantages including the production of hydrochloric acid and the presence of a considerable concentration of chlorine in the bromine obtained.
Other oxidants have been proposed. French Pat. No. 1,359,668 uses nitric acid as oxidant but this has disadvantages equal or greater than those of chlorine, involving destruction and regeneration of nitric oxides. The direct employ of oxygen itself is theoretically possible but temperatures as high as 800.degree.-1000.degree. C. are required for complete reaction, as indicated in Brit. Pat. No. 585,728.
When present applicants first considered using hydrogen peroxide to liberate bromine from bromides, they were discouraged by the statements of Pascal ("Nouveau traite de chimie minerale" Vol. XVI page 399 (Masson 1960).) indicating that the overall effect of contacting hydrobromic acid with hydrogen peroxide is the decomposition of the latter. Thus it is there stated "hydrogen peroxide undergoes on contact with hydrobromic acid solutions or acid solutions of bromides, a decomposition which causes the liberation of bromine. The phenomenon is due to a superimposition of two reactions: EQU H.sub.2 O.sub.2 +2Br.sup.- + 2H.sup.+ .fwdarw. 2H.sub.2 O+ Br.sub.2 EQU Br.sub.2 + H.sub.2 O.sub.2 .fwdarw. O.sub.2 +2Br.sup.- +2H.sup.+
at a given moment the two phenomena compensate each other: the hydrobromic acid oxidized at each instant is regenerated, the concentration of H.sup.+ ions remains constant and the total effect is that hydrogen peroxide undergoes decomposition."